In a nutshell, did the reformation take place because of changes in economic structure of society, or did the economic structure of society enable the reformation?
For Marx, religion is part of the process of alienation. The worker loses contact with the creation of his/her labour; instead of being an artisan crafting an object, s/he is a cog in a machine churning out commodities whose value s/he will not personally realize. In this process of alienation from ones species being, one becomes open to religion. For Weber, it is about meaning and context and interaction, and he introduces the notion of verstehen to discuss how protestantism becomes the 'spirit of capitalism'.
That's nowhere near enough, and it's a very long time since I did this stuff, but that's a simplified taster.